1. Field of the Invention
The present invention relates in general to integrated circuit (IC) testers of the type having a separate channel accessing each terminal of an IC being tested, and in particular to a tester that includes a disk drive in each channel as a source of test instructions.
2. Description of Related Art
A typical "per-pin" integrated circuit (IC) tester includes a separate channel for each terminal of an IC to be tested. Each channel includes a vector memory, a sequencer, a formatting circuit and a pin electronics circuit. The IC tester organizes a test into a succession of test cycles. Before the test, a host computer writes a sequence of vectors (data values) into successive addresses of the vector memory. Each vector defines the test activities the formatting and pin electronics circuits are to carry out during a test cycle. Such activities may include setting a test signal input to the DUT terminal to a particular state at a particular time during the test cycle or sampling a DUT output signal appearing at the DUT terminal at a particular time to determine if it is of an expected state. Before each test cycle the sequencer signals the vector memory to read out a vector to tell the formatting and pin electronics circuits what to do during the test cycle.
As ICs and the manner in which they are tested become more complex, the number of cycles per test increases, thereby increasing the size of the vector data sequence that must be stored in the channel's vector memories. Large high-speed vector memories are expensive. Also since it takes more time for a host computer to write a large vector sequence into the vector memory of each channel, the time required to program testers has increased. When a tester has to frequently alternate between two or more different tests, the time required to reprogram the tester limits its throughput.
What is needed is a tester having channels capable of economically storing large amounts of test instructions and which are capable of quickly switching from one type of test to another without requiring extensive reprogramming time.